This invention relates to a fuel injection control method for internal combustion engines at acceleration, and more particularly to a method of this kind which is intended to improve the driveability of the engine upon acceleration thereof.
A fuel injection control method for internal combustion engines is known, e.g. by Japanese Provisional Patent Publication (Kokai) No. 58-202335, which is adapted to determine the fuel injection quantity in dependence on operating parameters of the engine indicative of operating conditions of the engine, and which includes two modes of fuel injection, i.e. synchronous fuel injection wherein a fuel quantity determined based upon engine rotational speed and intake pipe absolute pressure is supplied through injection into the engine upon generation of each of control pulses generated at predetermined crank angle positions corresponding to respective suction stroke of the cylinders, and asynchronous fuel injection wherein a fuel quantity depending upon an accelerating condition of the engine is supplied through injection into the engine at timing irrespective of the timing of generation of the above control pulses when the engine is being accelerated.
According to the above known method, the synchronous fuel injection is sequentially effected for each of the cylinders to supply a fuel quantity dependent upon engine rotational speed and intake pipe absolute pressure to each of the cylinders, and on the other hand, an accelerating condition of the engine is detected by sensing the opening of a throttle valve in an intake pipe of the engine, and upon detection of the accelerating condition the asynchronous fuel injection is effected for all the cylinders at the same time to supply an accelerating fuel increment corresponding to the degree of opening of the throttle valve to each of the cylinders at one time, to thereby improve the responsiveness of fuel increase as well as improve atomization of fuel at engine acceleration.
According to this manner of fuel injection, the synchronous fuel injection of an increased fuel quantity corresponding to the degree of acceleration takes place immediately following the asynchronous fuel injection. As a consequence, the engine is eventually supplied with an excess of fuel equal to the accelerating fuel increments in addition to the actually required amount of fuel, which results in the air-fuel ratio of the resulting mixture supplied to the engine becoming overrich and hence in degraded engine output, thus impeding smooth acceleration of the engine.